This invention relates to blends of cycloaliphatic epoxy resins and epoxidized low viscosity polydiene polymers which are used for structural adhesives, coatings, electrical castings, encapsulants, potting compounds, laminates, and construction adhesives. More specifically, the invention relates to the use of epoxidized low viscosity polydiene polymers as toughening modifiers for cycloaliphatic epoxy resins.
Cycloaliphatic epoxy resins are generally known to be useful in a wide range of products such as filament-wound composites, as encapsulants for electrical products and in adhesives and coatings. Such resins include the Union Carbide Cycloaliphatic Epoxides and CYRACURE resins. Cycloaliphatic epoxy resins have the disadvantage that they are very brittle when cured. This brittleness makes them unsuitable for many applications including in coatings where brittleness leads to poor adhesion, in structural adhesives where brittleness causes poor impact resistance and in electrical encapsulants where brittleness leads to poor thermal shock resistance. Thus, it is clear that it would be advantageous if a way could be found to impart a degree of flexibility to these cycloaliphatic resins while retaining most, if not all, of their advantageous characteristics. The present invention provides this by blending the cycloaliphatic resins with specified low viscosity epoxidized polydienes.
Low viscosity epoxidized polydiene polymers are known to be useful in adhesives. Such polymers are described in commonly assigned U.S. Pat. No. 5,229,464. These polymers have a relatively high degree of flexibility and also a relatively high impact resistance. Compatible blends of the polymers of the above-described patent and aromatic epoxy resins are described in allowed copending commonly assigned application Ser. No. 08/090,856, filed Jul. 12, 1993, now U.S. Pat. No. 5,332,783. The epoxidized polydiene polymers impart a higher degree of flexibility to the aromatic epoxy resins when the two are blended together. The blends described in the afore-mentioned patent application have the disadvantage in that they are not sufficiently compatible at high concentrations of epoxidized polydiene polymer and also the toughness or impact resistance is good but could be improved upon.